This application claims the benefit of German patent application DE10114825.9, currently pending, which is incorporated herein by reference in its entirety.
The invention relates to a method and device for determining an operating temperature of a semiconductor component during operation, the semiconductor component comprising a PROM memory area which can be read from the outside, and a programming device for programming the PROM memory area of the semiconductor component.
In many semiconductor components it is important to determine the operating temperature. Thus, for example, when fabricating DRAMs precise knowledge of the junction temperature is highly significant for the planning and dimensioning of what is referred to as a guard band because the retention, and thus the determination of the refresh parameter depend on the junction temperature.
Sensors made of specific metals, doped semiconductors and alloys, from whose temperature-dependent resistance characteristic curve the temperature can be derived, are known for determining the operating temperature. Details on this can be found, for example, in Tietze Schenk, Halbleiter Schaltungstechnik [Semiconductor circuit technology], 9th edition 1991, chapter 26, Temperaturmessungen [Temperature measurements]. PT100, nickel-iron resistors or the platinum standard resistor are known as sensor types. Depending on the temperature range, the distinction is made between PTC thermistor sensors which cover the range between xe2x88x92100xc2x0 C. and 200xc2x0 C. and NTC thermistor sensors which cover the range between 1000xc2x0 C. and 7000xc2x0 C. During the fabrication of chips on a silicon base, the resistance characteristic curve of doped silicon is useful should one wish to measure the temperature on the chip. For silicon, the following is obtained as a relationship between the resistance and temperature
R=R25xc2x7(1+7.95xc2x710xe2x88x923(xcex94/xc2x0 C.)+1.95xc2x710xe2x88x925(xcex94/xc2x0 C.)2)
 being the temperature in xc2x0 C. and xcex94 being measured with respect to 25xc2x0 C., i.e. xcex94=xe2x88x9225xc2x0 C.
In order to make the measurement of the sensor resistance independent of the line resistances, a four-wire resistance measurement is generally carried out. However, when the chip temperature is determined externally, it is not possible to conclusively determine the silicon temperature because it depends on the thermal resistance of the chip housing and has a finite (even if small) thermal resistance. For this reason, the operating temperature of the silicon (junction temperature) is several degrees higher than at the surface of the housing. In order to be able to conclusively determine the silicon temperature, the junction temperature of a diode operated with an off voltage or a base-emitter path can be used. Here, two pins which can be tapped by the housing of the test specimen are used if they are accessible and do not impede the operation of the component. An advantage of this method is the simple external access during the measurement of the junction temperature in the silicon, but a disadvantage is that an electrical preparation has to be carried out for each test specimen and this preparation is costly or in some cases even impossible if the chip package does not have any wiring (Bord-On Chip/xcexcBGA Ball Grid Array/CSP Chip-Size Package). The measuring precision of the determination of the temperature is even often affected by loose contacts or thermal noise at the soldered connections, which is not compatible with a uniform, defined and largely disruption-free measuring specification for determining temperature.
In the RDRAM chip type from Rambus, for the first time a temperature sensor which is intended to test a limiting temperature and set a status bit at a specific threshold temperature was installed on a memory component. This switch-over point lies at approximately 90xc2x0 C. and is intended to mark the limit of the thermal loading of the chip. In order to determine the threshold temperature, the sensor in the RDRAM operates using the band-gap reference voltage which in principle is precisely defined and can be used for precisely determining the temperature limit. In reality, owing to the process fluctuations, the threshold temperature can be predicted only with an accuracy of 10%, for which reason a subsequent 4-bit-resolution soft-fuse option must also be used for precisely setting the threshold temperature of the sensor. A disadvantage with this way of determining the threshold temperature is that it is only possible to measure the junction between two temperature ranges, but not the absolute temperature.
The object of the invention is to provide a method with which the silicon temperature (junction temperature) on a semiconductor component can be measured, and a combined analog/digital measuring/transducer circuit, designed for said method, for performing integrated analog/digital on-chip temperature measurement in a simple, fast and space-saving fashion.
This object is achieved by means of the method according to claim 1 and the device according to claim 4. Preferred embodiments of the invention are the subject matter of the subclaims.
The invention is based on the idea that the time constant of a multivibrator which is intentionally made temperature-dependent should be used to generate trigger pulses. The number of trigger pulses which is thus temperature-dependent in a defined time interval is used as a clock generator for a counting unit and is thus a measure of the temperature. The temperature can thus be defined within the framework of the intrinsic measuring accuracy in an unambiguous and defined fashion.
The method according to the invention for determining an operating temperature of a semiconductor component during operation, the semiconductor component comprising a PROM memory area which can be read from the outside, and a programming device for programming the PROM memory area of the semiconductor component, is characterized by the steps: a) generation of a first temperature in the semiconductor component, b) generation of a measurement signal by a multivibrator which comprises a measuring circuit and a driver circuit, the frequency of the measurement signal depending on the temperature of the measuring circuit in the semiconductor component, c) sensing of the frequency of the measurement signal in a predefined measuring interval by means of a frequency counter, d) storage of the sensed frequency in the PROM memory area of the semiconductor component by the programming device, e) repetition of the steps b) to d) at a second temperature so that the frequency sensed at the first temperature and the frequency sensed at the second temperature are stored in the PROM memory area of the semiconductor component. The two frequency values can be used as calibration points for any further determination of the temperature.
The predefined measuring interval is preferably between 1 and 2 ms long and is predefined by a reference frequency which is applied externally to the semiconductor component and which is not temperature-dependent.
In a preferred embodiment of the invention, in addition to the respective counter reading, the first temperature and the second temperature are stored in the PROM memory area of the semiconductor component.
The device according to the invention for determining an operating temperature of a semiconductor component during operation, the semiconductor component comprising a PROM memory area which can be read from the outside, and a programming device for programming the PROM memory area of the semiconductor component, is characterized by a multivibrator for generating a measurement signal which comprises a measuring circuit and a driver circuit, the frequency of the measurement signal depending on the temperature of the measuring circuit in the semiconductor component, and a frequency counter for sensing the frequency of the measurement signal in a predefined measuring interval. The measuring interval is predefined externally and is thus independent of the temperature.
The measuring circuit in the semiconductor component for measuring temperature preferably comprises at least one diode, one transistor and/or one silicon resistor which are distributed over the region of the circuit on the chip or are arranged at thermally critical points of the circuit on the chip.
The measuring circuit in the semiconductor component preferably has a linear temperature/resistance characteristic curve.
The measuring circuit of the multivibrator in the semiconductor component particularly preferably has a greater temperature-dependence than the driver circuit of the multivibrator, which in particular has no temperature-dependence or only slight temperature-dependence.
The advantages of the circuit according to the invention are manifold. The measurement of the temperature is independent of process fluctuations during the manufacture of the circuit and does not need to be trimmed. The current temperature can be called at all times (by means of mode register set functions for DRAMs) from the temperature sensor which is calibrated once during the fabrication. In this way, the junction temperature can be determined during the chip fabrication on the wafer, component and module level and in the application without a high level of expenditure on measurement. Installed in various types of a product range of semiconductor components, with the circuit according to the invention the thermal properties of the components can be assessed by means of a uniform measuring method in the same way over the entire product range and above all uniformly in terms of fabrication and application. In addition, the temperature can be read at any time from the chip, even within the pattern run, on chip packages which are difficult to access and in the standard application if an appropriately oriented controller chip supports the interrogation of the temperature.
Further advantages are that an on-chip solution on silicon is possible and a temperature measurement can be activated during the fabrication and during tests of the component and is possible during operation (specifically in the mode register set function in the case of DRAMs); the temperature can (possibly after binary conversion) be output directly in a clocked fashion via a module pin and read off; a temperature standardization during fabrication by means of fuses with defined reference temperatures does not require any band-gap reference setting.
For the invention, no additional A/D converter is required for converting the analog measuring signal (for example a voltage) because a multivibrator functions as a temperature-dependent counting pulse transmitter only a small amount of space is therefore required on the chip for the circuit according to the invention. Even a plurality of addressable sensors (RC elements/diodes) can be integrated for one chip.